1. Field of the Invention
The present invention relates to new cure accelerator systems for anaerobic curable compositions. These anaerobic cure systems include the combination of a cationic initiator and a reducing agent, plus either (a) an aromatic nitrogen-containing compound and a thiol or (b) acetyl phenyl hydrazine (“APH”).
2. Brief Description of Related Technology
Anaerobic adhesive compositions generally are well-known. See e.g., R. D. Rich, “Anaerobic Adhesives” in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker, Inc., New York (1994), and references cited therein. Their uses are legion and new applications continue to be developed.
Conventional anaerobic adhesives ordinarily include a free-radically polymerizable acrylate ester monomer, together with a peroxy initiator and an inhibitor component. Oftentimes, such anaerobic adhesive compositions also contain accelerator components to increase the speed with which the composition cures.
Desirable anaerobic cure-inducing compositions to induce and accelerate cure may include saccharin, toluidines, such as N,N-diethyl-p-toluidine (“DE-p-T”) and N,N-dimethyl-o-toluidine (“DM-o-T”), APH, maleic acid (“MA”), and quinones, such as napthaquinone and anthraquinone. See e.g. U.S. Pat. Nos. 3,218,305, 4,180,640, 4,287,330 and 4,321,349.
Saccharin and APH have been used as standard cure accelerator components in anaerobic adhesive cure systems since the inception of the technology, and have been well studied in that connection. Hitherto, it was believed that the nitrogen-hydrogen bond off the heterocycle ring was nessecary to achieve performance under anaerobic conditions, as early studies substituting the hydrogen with an alkyl group proved to be ineffective. See F. J. Boerio et al., “Surface-Enhanced Raman Scattering from Model Acrylic Adhesive Systems”, Langmuir, 6, 721-27 (1990), in which it is stated “[t]hese salts [of saccharin] are thought to be important factors in the curing reaction of the adhesive.”
Recently, Henkel Corporation was granted a series of U.S. patents that define anaerobic cure accelerator compounds. U.S. Pat. No. 6,835,762, which defines an invention directed to an anaerobic curable composition, comprises:                (a) a (meth)acrylate component;        (b) an anaerobic cure-inducing composition; and        (c) an anaerobic cure accelerator compound having the linkage —C(═O)—NH—NH— and an organic acid group on the same molecule. The composition is substantially free of acetyl phenyl hydrazine and maleic acid, and the anaerobic cure accelerator compound excludes 1-(2-carboxyacryloyl)-2-phenylhydrazine.        
U.S. Pat. No. 6,897,277 is directed to and claims an anaerobic curable compositions, comprising:                (a) a (meth)acrylate component;        (b) an anaerobic cure-inducing composition substantially free of saccharin; and        (c) an anaerobic cure accelerator compound within the following structure        
where R is selected hydrogen, halogen, alkyl, alkenyl, hydroxyalkyl, hydroxyalkenyl, carboxyl, or sulfonato, and R1 is selected from of hydrogen, alkyl, alkenyl, hydroxyalkyl, hydroxyalkenyl, or aralkyl.
U.S. Pat. No. 6,958,368 is directed to and claims an anaerobic curable composition, comprising:                (a) a (meth)acrylate component;        (b) an anaerobic cure-inducing composition substantially free of saccharin; and        (c) an anaerobic cure accelerator compound within the following structure        
where Y is an aromatic ring, optionally substituted at up to five positions by C1-6 alkyl or alkoxy, or halo groups; A is C═O, S═O or O═S═O; X is NH, O or S and Z is an aromatic ring, optionally substituted at up to five positions by C1-6 alkyl or alkoxy, or halo groups, or Y and Z taken together may join to taken together may join to the same aromatic ring or aromatic ring system, provided that when X is NH, o-benzoic sulfimide is excluded from that structure.
In J. V. Crivello et al., “Redox Cationic Polymerization: The Diaryliodonium Salt/Ascorbate Redox Couple”, J. Polym. Sci., 19, 539-48 (1981), the development and use of the diaryliodonium salt/ascorbate redox couple in the polymerization of several types of cationically polymerizable monomers is described. Chief among those monomers is epoxy.
U.S. Pat. No. 4,656,229 describes a two-part anaerobic adhesive that uses in the one part a diaryliodonium salt and in a second part the condensation reaction product of an aldehyde and a primary amine.
U.S. Pat. Nos. 4,413,108, 4,500,608, and 4,528,059 each speak to the use of triazine and thiols to facilitate anaerobic cure of adhesive compositions.
Notwithstanding the foregoing, there continues to be an on-going desire to find alternative technologies for accelerating the cure of anaerobic curable compositions, to differentiate existing products and provide supply assurances in the event of shortages or cessation of supply of raw materials. Accordingly, it would be desirable to identify new materials, which function as anaerobic cure systems for anaerobic curable compositions.